Volume 64 No. 03 May 16, 2019

WEATHER & PESTS

Rainfall diminished from the previous week and a warm-ing trend began, favoring an acceleration of fieldwork throughout Wisconsin after significant early-season delays. Mild and mostly dry weather afforded growers a larger window for field activities compared to recent weeks, and both spring tillage and planting advanced as rapidly as could be expected. Despite improved temper-atures and soil moisture conditions, planting progress for corn, oats, soybeans and vegetable crops remained well behind normal. At the start of the week, only 14% of the state’s intended corn acreage had been planted, 11 days behind average and the slowest pace since 2013. Meanwhile, most farmers have yet to begin planting soybeans, with only 4% of this year’s acres in the ground. A continuation of warm, dry weather is needed to offset spring planting delays, but the 10-day forecast calls for the opposite.

LOOKING AHEAD

BLACK CUTWORM: Development of black cutworm larvae appears well synchronized with corn emergence this spring, and infestations are anticipated to begin in about two weeks. Based on the black cutworm degree-day model, 119 heat units (modified base 50°F), or about 10 calendar days, remain before larvae in the Beloit area of Rock County Wisconsin reach the damaging fourth-

instar stage. The peak corn-cutting window is now fore-cast to open by May 25 for south-central and south-western Wisconsin, two days earlier than last predicted. ALFALFA WEEVIL: Larvae are expected to emerge in advanced alfalfa fields in the week ahead. Regular scouting is advised beginning at 300 degree days (sine base 48°F), or by May 20 in the southern counties. Scouting should start on May 27 in the central counties, where May temperatures have been abnormally low. CODLING MOTH: Apple growers in the DATCP trap- ping network are reminded to begin daily pheromone trap checks to determine the date of the first sustained capture of moths on consecutive nights, referred to as the biofix. This event is probable next week in parts of southern Wisconsin. GYPSY MOTH: The first aerial treatments of the season are tentatively planned for May 21 in Green and Lafayette counties. Approximately 23,600 acres are scheduled to receive an application of Bacillus thuringiensis var. kurstaki, or Btk. Aerial spraying is weather-dependent. Conditions such as fog, high winds, rain predicted within four hours, or high humidity can delay spray plans. VIBURNUM LEAF BEETLE: Newly-hatched larvae were collected last week from viburnum in Milwaukee County. Milwaukee is one of six Wisconsin counties in which

PEST BULLETIN WISCONSIN

Timely crop pest news, forecasts, and growing season conditions for Wisconsin

STATE OF WISCONSIN DEPARTMENT OF AGRICULTURE, TRADE AND CONSUMER PROTECTION PLANT INDUSTRY BUREAU 2811 Agriculture Dr. Madison, WI 53718 ● http://pestbulletin.wisconsin.gov

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viburnum leaf beetle has been detected since 2009, in addition to Kenosha, Ozaukee, Waukesha, Washington and Winnebago. Gardeners, landscapers, nursery stock growers and retailers in southeastern Wisconsin should be on alert for the distinctive skeletonization of viburnum leaves caused by this insect and report sightings to DATCP or the UW Insect Diagnostic Lab.

PLUM CURCULIO: Degree day accumulations in the warmest southern areas of the state will soon be appro-priate for weevil activity. A mean daily temperature of 60°F or more for 3-4 days prompts the spring emer-gence and migration of overwintered weevils into the orchard perimeter. EUROPEAN CORN BORER: Pupation of carryover larvae from last season is beginning in south-central and south-western Wisconsin. According to the results of 2018 ECB abundance survey, the fall larval population decreased to 0.01 borer per plant, the lowest state average recorded in 77 years. A very small spring moth flight should be expected next month.

FORAGES & GRAINS

ALFALFA WEEVIL: Adults are appearing in very low num-bers in alfalfa. The first small larvae should be detectable in advanced fields by May 20. PEA APHID: Surveys this week found very low counts of 1-35 aphids per 100 sweeps. The average was 17 per 100 sweeps. Pea aphid development is favored by cool, dry weather, with populations increasing most rapidly at temperatures around 65°F. Heavy early-season aphid

DEGREE DAYS JANUARY 1 - MAY 15 density can cause stunting of the first crop and damage to subsequent cuttings. Pea aphids are also suspected of transmitting certain alfalfa virus diseases. TARNISHED PLANT BUG: Alfalfa sampled in Columbia, Dane, Grant, Green, Iowa, Lafayette and Rock counties had low counts of 1-7 per 100 sweeps. Plant bug abun-dance in the first-crop alfalfa is an indicator of potential high populations in apples, strawberries and other fruits and vegetables.

CORN

BLACK CUTWORM: Larvae produced by migrants that arrived in mid-April should grow large enough to begin cutting emerging corn plants by May 25 in advanced southern and western areas of the state. The cutting period is forecast to open by June 1 in central Wisconsin. A decrease in the number of moths captured in survey traps during the May 9-15 reporting period signals that

LOCATION 50°F 2018 NORM 40°F Dubuque, IA 258 346 361 611

Lone Rock 262 303 ― 578 Beloit 245 301 371 560 Sullivan 224 248 322 503 Madison 236 282 346 555 Juneau 195 250 ― 456 Racine 168 220 ― 426 Waukesha 208 226 ― 486 Milwaukee 181 226 272 449 Hartford 196 238 ― 457 Appleton 160 222 ― 406 Green Bay 148 212 265 390 Big Flats 197 258 ― 464 Hancock 179 223 334 430 Port Edwards 183 226 325 430 La Crosse 218 306 384 532 Eau Claire 198 269 330 464 Cumberland 142 203 278 341 Bayfield 90 72 ― 269 Wausau 134 201 276 328 Medford 129 195 241 317 Crivitz 139 222 ― 358 Crandon 124 188 222 310 Method: Modified B50; Modified B40 as of January 1, 2019. NORMALS based on 30-year average daily temps, 1981-2010.

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the migration has slowed, though weedy field conditions remain highly favorable for egg laying. The spring migra-tion, which started around April 4, has to date yielded a cumulative count of 867 moths in 44 traps. Approximately 1,162 moths in 47 traps had been collected by this time last year. Based on significant planting delays, late weed control, and consistent, moderate moth flights, much of the state's corn acreage is considered to be at high risk of cutworm infestation this spring.

TRUE ARMYWORM: Moths have been arriving for at least five weeks and continue to be collected in black light traps. The trap at Janesville in Rock County has reported significant weekly counts as high as 67 moths per trap since April 11. The recent capture of moths as far north as Marshfield confirms that the migration has extended into Central Wisconsin. First-generation armyworm larvae usually become noticeable in alfalfa fields by late May and in corn by early to mid-June. The success of the first generation will lay the foundation for the second generation in July. WIREWORM: Corn planted into fields formerly in grassy alfalfa, pasture or sod is at an increased risk of wireworm damage, which is especially important to consider this spring as winterkilled alfalfa acreage is replaced with

corn. Wireworm larvae feed on the roots of grasses and germinating crop seeds. Symptoms are missing, wilted, or stunted seedlings and young plants. If wireworm damage is suspected, growers or consultants should dig up several ungerminated seeds or damaged plants along with a four to six inch core of surrounding soil to check for wireworms in and around roots, or in the underground portion of stems. Larvae may be extracted from soil by washing. Control options are limited and include disking up the affected portion of the field, treating with a soil insecticide and replanting.

FRUITS

PLUM CURCULIO: Adult emergence and oviposition are forecast to begin in the week ahead. This weevil usually emerges around 250 degree days (base 50°F), and mi-grates into the orchard perimeter when temperatures consistently exceed 60°F. Central and northern orchards are still 60-120 degree days or about 5-10 calendar days from first emergence of plum curculio.

CODLING MOTH: The spring moth flight is likely to start next week in locations where temperatures at dusk ex-ceed 62°F. Frequent trap monitoring will be required to document the “biofix” or sustained capture of moths. Apple growers in northern Wisconsin can expect to see moths during the last week of May. SPOTTED TENTIFORM LEAFMINER: Moths flights have been underway since mid-April and peak emergence has occurred at some sites. The most targeted scouting window for sapfeeder larvae is two weeks after a peak catch in pheromone traps. Counts during the week

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ending May 15 ranged as high as 1,230 moths per trap, with the largest captures reported from Marquette and Marathon counties. These elevated counts (>1,000 moths) signal that the flight has probably peaked near Edgar and Montello. OBLIQUEBANDED LEAFROLLER: Larvae have resumed activity after overwintering under the bark of scaffold limbs and twigs. The yellowish-green caterpillars with black head capsules typically feed for 2-3 weeks before pupating inside rolled leaves. Scouting should begin next week.

REDBANDED LEAFROLLER: Larvae are appearing in southern and central orchards where 228 degree days (simple base 45°F) have been surpassed. The coopera-tor at Hill Point in Sauk County confirmed that small larvae have been observed feeding on new foliage, while slightly larger caterpillars can be found in folded leaves. The first RBLR caterpillars generally appear around petal fall, which is when scouting should start. RBLR larvae, in contrast to OBLR larvae, are uniformly yellowish-green and do not have black heads. SPRING CATERPILLARS: Development of resident orchard caterpillars has accelerated with warmer temperatures. Species commonly found on growing terminals and in blossoms at this time of year include the green fruitworm, obliquebanded leafroller (OBLR), redbanded leafroller (RBLR), spring cankerworm, and variegated leafroller. Bt products such as Agree, Deliver or Dipel may be applied for control only if the weather is sufficiently warm for cat-erpillar feeding and blossoms are open. Because Bt must be consumed by the larvae to be effective, warm temp-eratures are required in the three-day post-spray period

to achieve satisfactory mortality. Preferred conditions for Bt applications are when the weather is consistently warm (~60°F) and sunny. EUROPEAN RED MITE: The first hatch of European red mite (ERM) is expected soon. For orchards with past mite problems, scouting previous hotspots for young mites on spur leaves and eggs at the base of fruiting spurs is suggested. Apple trees with early ERM activity should be flagged and resampled in early June to determine if levels are above-threshold and a miticide treatment is warranted. ROSY APPLE APHID: Early colonies should become ap-parent next week. Rosy apple aphids are cultivar-specific, therefore scouting efforts should focus on blocks or va-rieties with a history of aphid damage. Do not treat for aphids if trees are in bloom.

VEGETABLES

LATE BLIGHT: Potato growers are reminded that Wiscon-sin Administrative Code (ATCP 21.15(2)) requires potato cull piles to be fed, disked in, or otherwise removed by May 20 to prevent late blight from developing on volun-teer plants. This disease was significantly less prevalent last season than in 2017. Three counties—Adams, Marquette and Waushara—had confirmed cases in 2018 compared to 13 counties the year before. SEEDCORN MAGGOT: First-generation fly emergence has peaked throughout the southern two-thirds of the state. Emergence should peak next week in areas north of Wausau, where 360 degree days (sine base 39°F) will

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be surpassed. A key cultural control for SCM is to plant during “fly-free” pupal stage between generations, around 846 degree days. Beloit should reach the fly-free window by May 26, while flies in the Hancock area should begin pupating by June 2.

ONION MAGGOT: Flies of the first and most damaging generation will likely begin emerging next week in south-ern Wisconsin. Preventive measures, including crop rotation and removal of onion cull piles, are particularly important for minimizing risk of infestation. Granular furrow treatments offer good control, provided the rate is correct and the insecticide is properly applied in the furrow at seeding. Chemical control may be appropriate if maggot damage to the last season’s crop exceeded 5-10%. For home gardeners, rotating this year's onion plantings as far as possible from last year's is suggested to reduce the threat of maggot damage. WIREWORM: The cool, wet soils prevalent this spring are favorable for wireworms, subterranean pests with a broad host range that includes beans, beets, cabbage, carrots, corn, lettuce, onion, peas, potatoes, radishes, sorghum, soybeans, as well as herbaceous ornamentals. Wireworm larvae feed on seeds and on the roots of plants, impairing germination and causing plants to wilt.

One indicator of wireworm activity is dead spots scattered throughout a planting. In situations where wireworm feeding is suspected, growers should dig up several un-germinated seeds or wilted plants from affected areas to verify wireworm larvae as the causal pest.

NURSERY & FOREST

CREEPING JENNY: This invasive species was recently found by inspectors at two southwestern Wisconsin nursery dealers. Creeping Jenny, or moneywort, is a “restricted” plant under the Chapter NR40 Wisconsin invasive species rule. Restricted plants are defined as already established in the state and have caused or have the potential to cause “significant environmental or eco-nomic harm”. The cultivar creeping Jenny ‘Aurea’ and yellow and gold leaf forms are not considered invasive and are exceptions to the rule.

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BOXWOOD BLIGHT: This devastating fungal disease was found on “Korean” boxwoods earlier this month in a Dane County nursery. A Pest Abatement Order directing the removal and destruction of all boxwood plants of the same variety and from the same source was issued in response. This is the first Dane County interception of boxwood blight. The disease was previously found in a Kenosha County nursery last August. Symptoms of boxwood blight are similar to other com-mon boxwood diseases of such as Volutella blight, mak-ing laboratory diagnosis imperative. The brown spots that initially appear on the leaves eventually coalesce and lead to defoliation, while infected stems develop dark lesions. White fungal spores can also be seen without magnification on the undersides of infected leaves and on stem lesions. Spores may remain viable for six years on plant debris and in the soil.

Movement of infected nursery stock, tools and equipment is the primary pathway by which the disease spreads. Purchasing boxwoods from clean sources that have been inspected or tested for boxwood blight is strongly advised. Newly-purchased plants or cuttings should be isolated and kept under observation for a minimum of four weeks. During this period, fungicides should not be used. If box-wood blight is suspected, contacting your county Exten-sion office is recommended. Additional information is available on the DATCP Boxwood Blight page. VIBURNUM LEAF BEETLE: Larvae of this relatively new pest to Wisconsin were reported to have hatched near Milwaukee during the week beginning May 5. This in-vasive defoliator has now been found in six southeast-ern counties since 2009, including Kenosha, Milwaukee,

Ozaukee, Waukesha, Washington and Winnebago. As its name suggests, the viburnum leaf beetle feeds exclus-ively on viburnums, completing one generation per year beginning with egg hatch in spring. The larvae now emerging will consume foliage until they pupate in the soil next month. The adults emerge in mid-summer. Viburnum leaf beetle is particularly damaging because successive feeding by larvae and adults pre-vents shrubs from refoliating and can kill healthy plants after 2-3 years of heavy infestation.

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APPLE INSECT & BLACK LIGHT TRAP COUNTS MAY 9 - 15

COUNTY SITE STLM1 RBLR2 CM3 OBLR4 DWB5 LPTB6 BMSB7 AM RED8 YELLOW9

Bayfield Keystone 0 0 ―― ―― Bayfield Orienta ―― ―― ―― ―― Brown Oneida 43 51 0 ―― Columbia Rio 0 125 0 0 0 Crawford Gays Mills ―― ―― ―― ―― Dane DeForest ―― ―― ―― ―― Dane Mt. Horeb 25 ―― ―― ―― 7 Dane Stoughton 10 40 0 0 0 Fond du Lac Campbellsport 21 24 0 0 5 Fond du Lac Malone 14 64 0 ―― 0 Fond du Lac Rosendale 1 17 ―― ―― Grant Sinsinawa 82 49 ―― ―― Green Brodhead 9 6 0 14 0 Iowa Mineral Point 223 46 0 2 Jackson Hixton 31 43 0 0 0 Kenosha Burlington 30 31 0 0 Marathon Edgar 1130 76 ―― ―― 0 Marinette Niagara 0 7 ―― ―― Marquette Montello 1230 11 0 0 0 Ozaukee Mequon 4 9 0 12 0 Pierce Beldenville 212 30 0 0 0 Pierce Spring Valley 11 29 ―― ―― Racine Raymond 40 0 ―― ―― Racine Rochester 37 17 ―― ―― Richland Hill Point 32 28 0 ―― 0 Sheboygan Plymouth 615 37 ―― ―― 0 Walworth East Troy 30 23 0 ―― Walworth Elkhorn 15 45 0 ―― Waukesha New Berlin 12 0 ―― ――

1Spotted tentiform leafminer; 2Redbanded leafroller; 3Codling moth; 4Obliquebanded leafroller; 5Lesser peachtree borer; 6Dogwood borer; 7Brown marmorated stink bug; 8Apple maggot red ball; *Unbaited; **Baited; 9Apple maggot yellow board.

COUNTY SITE BCW1 CEL2 CE3 DCW4 ECB5 FORL6 SCW7 TA8 VCW9 WBC10

Columbia Arlington 0 0 0 0 0 0 0 4 0 0 Columbia Pardeeville 0 0 0 0 0 4 0 4 1 0 Dodge Beaver Dam 1 0 0 0 0 0 0 2 0 0 Fond du Lac Ripon 0 0 0 0 0 0 0 1 0 0 Grant Prairie du Chien 0 0 0 0 0 0 0 0 0 0 Manitowoc Manitowoc 0 0 0 0 0 0 0 6 0 0 Marathon Wausau ―― ―― ―― ―― ―― ―― ―― ―― ―― ―― Monroe Sparta 0 0 0 0 0 1 0 0 0 0 Rock Janesville 0 0 0 0 0 0 0 15 0 0 Walworth East Troy 0 0 0 0 0 0 0 4 0 0 Wood Marshfield 0 0 0 0 0 0 0 4 1 0

1Black cutworm; 2Celery looper; 3Corn earworm; 4Dingy cutworm; 5European corn borer; 6Forage looper; 7Spotted cutworm; 8True armyworm; 9Variegated cutworm; 10Western bean cutworm.

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BLACK CUTWORM PHEROMONE TRAP COUNTS 2019

COUNTY SITE WEEK 1 WEEK 2 WEEK 3 WEEK 4 WEEK 5 WEEK 6 WEEK 7 WEEK 8

Adams Brooks ―― 0 ―― 0 0 1 Adams Grand Marsh ―― 0 ―― 0 0 0 Buffalo Alma 0 0 0 0 3 1 Buffalo Gilmanton 0 0 1 0 2 2 Columbia Columbus 0 1 3 3 4 0 Columbia Hampden 1 12* 13* 7 20* 4 Columbia Leeds 0 6 0 3 4 1 Dane Blooming Grove 0 1 4 1 2 0 Dane Blue Mounds 1 0 2 3 1 5 Dane Cross Plains 7 1 0 5 8 2 Dane Deerfield 3 8 3 5 9 2 Dane Middleton 0 0 0 1 2 1 Dane Springfield 0 0 6 13* 15* 7 Dane Vienna 0 0 0 3 4 0 Dodge Beaver Dam 0 1 9 12* 12* 1 Dodge Calamus 0 9 5 3 12* 7 Dodge Hubbard 0 8 5 4 5 1 Dodge Lowell 0 3 5 1 0 2 Dodge Oak Grove 0 3 2 6 2 4 Dodge Waupun 0 7 7 13* 19* 3 Door Sturgeon Bay ―― ―― 1 5 5 2 Fond du Lac Lamartine 0 0 7 3 1 3 Fond du Lac Ripon 1 1 20* 9 11 1 Grant Dickeyville 0 0 6 7 2 4 Grant Platteville 1 0 3 15* 13* 5 Grant Prairie du Chien 0 0 0 2 0 4 Iowa Brigham E 0 0 1 3 14* 0 Iowa Brigham W 1 0 8 2 13* 8 Iowa Dodgeville E 1 1 2 14* 7 6 Iowa Dodgeville W 0 0 6 9 4 4 Iowa Mineral Point E 0 0 7 6 18* 3 Iowa Mineral Point W 0 0 3 5 14* 3 Jefferson Ixonia E 0 9 14* 13* 6 4 Jefferson Ixonia W 2 15* 2 4 7 7 Jefferson Johnson Creek 1 7 2 0 0 1 Jefferson Milford 0 3 0 2 3 0 Kewaunee Algoma ―― ―― 0 0 2 4 La Crosse West Salem ―― ―― ―― ―― 2 0 Lafayette Belmont 0 0 3 3 6 3 Lafayette Kendall 0 0 4 7 4 1 Pepin Durand ―― 0 0 2 6 ―― Rock Janesville 5 11* 3 3 4 2 Washington North Lake 1 6 0 0 0 0 Waukesha Oconomowoc 0 4 2 1 1 0

*Intense capture occurs when 9 or more moths are caught in a 2-night period. Week 1 (April 4-10), Week 2 (April 11-17), Week 3 (April 18-24), Week 4 (April 25-May 1), Week 5 (May 2-8), Week 6 (May 9-15), Week 7 (May 16-22), Week 8 (May 23-29).